Tables 205-207. 



TABLE 206. — Platinum Besistance Thermometers, 



195 



Callendar has shown that if we define the platinum temperature, pt, by pt = ioo-{ (R — Rq) 

 /(Rioo — Ro) }■ , where R is the observed resistance at t° C, Rq that at 0°, Rioo at 100°, then the re- 

 lation between the platinum temperature and the temperature t on the scale of the gas thermo- 

 meter is represented by t — pt = 5-{ t/ 100 — i ^■t/ioo where 8 is a constant for any given sample 

 of platinum and about 1.50 for pure platinum (impure platinum having higher values). This holds 

 good between — 23° and 450° when S has been determined by the boiling point of sulphur (445°.) 



See Waidner and Burgess, Bui. Bureau Standards, 6, p. 149, 1909. Also Bureau reprints 124, 

 143 and 149- 



TABLE 806.— Thermodynamic Temperature of the Ice Point, and Reduction to 

 Thermodynamic Scale. 



Mean = 273.1° C. (ice point). 



For a discussion of the various values and for the corrections of the various gas thermometers to 

 the thermodynamic scale see Buckingham, Bull. Bureau Standards, 3, p. 237, 1907. 

 Scale Oorrections tor Oas Thennometen. 



See also Appendix, p. 438. 

 TABLE 207. — Standard Points for the Calibration of Thermometers, 



• Thermoelectric extrapolation, t Optical extrapolation. 

 (Day and Sosman, Journal de Physique, 19 12. Mesure des temperatures elevfees.) A few additional points 

 are: H, boils— 252.6=; O, boils — 182.7°; COj, sublimes — 78.5°; Hg. freezes — 38.87°; Alumina melts 2000°; 

 Tungsten melts 3400'. Quartz, a to ft change, 573.3" ± ». 



Smithsonian Tables. 



